The principle of the so-called dry cell is well known, and the construction of commerical dry cells is somewhat fairly well standarized as evidenced by the disclosure in the textbook titled "Batteries" edited by Karl V. Kordesch -- Marcel Dekker, Inc. New York publishers -- 1974 and the textbook titled "Primary Batteries" by George W. Vinal -- John Wiley and Sons, Inc., New York publishers -- 1951.
The term "dry cell" implies that the electrolyte of the cell is immobilized, much of it being contained or absorbed by a layer of material interposed between the anode and cathode of the cell. This layer is generally referred to as the separator and is a physical member or structure which retains the electrolyte solution and provides a means for maintaining the anode in working engagement with the cathode while at the same time maintaining physical separation between the anode and the cathode, said cathode, usually in a mix form.
Examples of commercial dry cells on the market today include such cells as the Leclanche cell, the zinc chloride cell and the magnesium cell. These cells basically comprise an anode, a cathode-depolarizer mix and an electrolyte between the cathode-depolarizer mix and the anode. A conventional cylindrical dry cell is made up of a container of an anodic metal high in the electromotive series, such as zinc, magnesium or alloys thereof, which serves as the anode, a depolarizer mix generally containing a reducible chemical compound, particulate conductive material and an aqueous solution of an ionic conductive material (electrolyte) chosen with regard to the nature of the cathodic and anodic materials, and a separator, also containing the electrolyte, positioned between the anode and the cathode-depolarizer mix.
It is well known in the art to fabricate dry cell separators from various gelatinous paste-type materials formed from starch, flour, or methyl cellulose, which may each be used either unsupported or supported by paper or similar backing or substrate material.
The cathode-depolarizer mix is generally in the form of a core or bobbin which is molded under pressure to an exact diameter and height to accommodate a specific cell size. The diameter of the bobbin is molded less than that of the interior of the anode container by an amount sufficient to provide a space therebetween to accommodate the electolyte, said electrolyte usually in the form of a paste containing an ionic conductive material chosen with respect to the nature of the cathodic and anodic materials of the cell and a stiffening agent or gelatinous medium such as starch with or without flour. The cathode-depolarizer mix may be molded around a conductive rod, such as a carbon rod, or the conductive rod may be driven through the mass of the mix after it has been formed. The conductive rod, sometimes referred to as the positive electrode, is not strictly an electrode but rather a collector and conductor of electric current from the cathode to the positive terminal external of the cell.
Upon being ejected from the mold, the bobbins are assembled into the anode containers. Care is required in the handling of bobbins since any mechanical injury, even to a slight degree, can result in cracking and chipping of the mix forming the bobbins. In fact, the accidental striking of the bobbins against foreign objects or even severe jarring of the bobbins during their assembly has resulted in chipping and breaking of the bobbins to an extent that such chips and broken bobbins account for a sizable amount of the depolarizer mix that is classified as waste or scrap. In addition to the economic loss due to excessive waste of the depolarizer mix because of chipping and breaking of bobbins during their assembly, the cells assembled with chipped or broken bobbins are deprived of reducible material thereby possibly shortening the useful life of such cells.
It is not only the bobbin mix that must be handled with care to prevent the mix from cracking and chipping, but any depolarizer mix that is formed into a discrete body, no matter how small, and which is subject to handling before and/or during assembly, will require gentle handling if cracking, chipping and/or breaking of the mix is to be minimized. Thus the depolarizer mix that is formed into small discrete slugs which are fed into a separator-lined anode container and then tamped before, after, or during the insertion of the carbon rod to form the bobbin in place, also requires special handling since it too is subject to cracking and/or breaking when subject to mechanical injury.
Another form of depolarizer mix body requiring special handling is called a mix cake which is used in what are commonly called flat cells, such as the "Mini'Max" type cells. The mix cake is usually a square, rectangular, or circular shaped molded body comprising the same components of the depolarizer mix used in the cylindrical type cells. The problems encountered in handling the mix cakes are the same as those recited above for the molded bobbins.
An object of the present invention is to provide an improved cathode-depolarizer mix for galvanic cells.
Another object of the present invention is to provide a discrete body of a cathode-depolarizer mix that will substantially resist chipping and/or breaking when mechanically injured.
Another object of the present invention is to provide an improved binder for various cathode-depolarizer mixes which are formed into bobbins, mix cakes or similar bodies.
Another object of the present invention is to provide an improved cathode-depolarizer mix which contains a minor amount of polyacrylamide binder.
Another object of the present invention is to provide a process for making an improved cathode-depolarizer mix which contains a minor amount of a polyacrylamide binder.